package DFS_BFS;

/**
 * @PackageName: DFS_BFS
 * @ClassName: LeetCode200
 * @Author: chen jinxu
 * @Date: 2022/2/9 22:25
 * @Description: //岛屿数量
 *      给你一个由 '1'（陆地）和 '0'（水）组成的的二维网格，请你计算网格中岛屿的数量。
 * 岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。
 * 此外，你可以假设该网格的四条边均被水包围。
输入：grid = [
['1','1','1','1','0'],
['1','1','0','1','0'],
['1','1','0','0','0'],
['0','0','0','0','0']
]
输出：1

输入：grid = [
['1','1','0','0','0'],
['1','1','0','0','0'],
['0','0','1','0','0'],
['0','0','0','1','1']
]
输出：3
链接：https://leetcode-cn.com/problems/number-of-islands
 */
public class LeetCode200 {
    public static void main(String[] args) {
        char[][] grid1 = {
                {'1','1','1','1','0'},
                {'1','1','0','1','0'},
                {'1','1','0','0','0'},
                {'0','0','0','0','0'}};
        int result1 = numIslands(grid1);
        System.out.println(result1);
        char[][] grid2 = {
                {'1','1','0','0','0'},
                {'1','1','0','0','0'},
                {'0','0','1','0','0'},
                {'0','0','0','1','1'}};
        int result2 = numIslands(grid2);
        System.out.println(result2);

    }

    public static int numIslands(char[][] grid) {
        if (grid == null || grid.length == 0) {
            return 0;
        }
        int nr = grid.length;
        int nc = grid[0].length;
        int num_isLands = 0;
        for (int r = 0; r < nr; r++) {
            for (int c = 0; c < nc; c++) {
                if (grid[r][c] == '1') {
                    num_isLands++;
                    dfs(grid, r, c);
                }
            }
        }
        return num_isLands;
    }

    private static void dfs(char[][] grid, int r, int c) {
        int nr = grid.length;
        int nc = grid[0].length;
        if (r < 0 || c < 0 || r >= nr || c >= nc || grid[r][c] == '0') {
            return;
        }
        grid[r][c] = '0';
        dfs(grid, r + 1, c);
        dfs(grid, r - 1, c);
        dfs(grid, r, c + 1);
        dfs(grid, r, c - 1);
    }

}
